diff --git a/internal/auth/web.go b/internal/auth/web.go
index 3c13372..3e94301 100644
--- a/internal/auth/web.go
+++ b/internal/auth/web.go
@@ -80,9 +80,15 @@ func (s *Handlers) credentialRoutes(r chi.Router) {
 	authLimit := web.NewRateLimiter(10, 6*time.Second)
 	r.With(authLimit.Middleware).Post("/login/password", s.Auth.LoginPassword)
 	r.With(authLimit.Middleware).Post("/signup/password", s.Auth.SignupPassword)
-	r.Post("/api/register/begin", s.Auth.RegisterBegin)
+	// The user-initiated WebAuthn "begin" ceremonies share the same per-IP
+	// credential-attempt bucket: register/begin persists an account row (unbounded
+	// spam would flood the users table and squat usernames) and login/begin is a
+	// username oracle. The finish steps require an in-progress ceremony, and
+	// discoverable/begin auto-fires on page load (passive autofill) and writes
+	// nothing, so those stay unthrottled.
+	r.With(authLimit.Middleware).Post("/api/register/begin", s.Auth.RegisterBegin)
 	r.Post("/api/register/finish", s.Auth.RegisterFinish)
-	r.Post("/api/login/begin", s.Auth.LoginBegin)
+	r.With(authLimit.Middleware).Post("/api/login/begin", s.Auth.LoginBegin)
 	r.Post("/api/login/finish", s.Auth.LoginFinish)
 	r.Post("/api/login/discoverable/begin", s.Auth.LoginDiscoverableBegin)
 	r.Post("/api/login/discoverable/finish", s.Auth.LoginDiscoverableFinish)
diff --git a/internal/core/endpoints_auth_test.go b/internal/core/endpoints_auth_test.go
index 3e21fcf..ba3208c 100644
--- a/internal/core/endpoints_auth_test.go
+++ b/internal/core/endpoints_auth_test.go
@@ -61,6 +61,39 @@ func TestPasswordSignupAndLogin(t *testing.T) {
 	}
 }
 
+// TestWebAuthnBeginRateLimited: the user-initiated passkey "begin" ceremonies
+// share the credential-attempt limiter. register/begin persists an account row,
+// so an unthrottled loop would flood the users table and squat usernames; this
+// is a regression guard for the pre-release audit finding that they were
+// unlimited. A malformed body 400s in the handler, but the limiter middleware
+// runs first — which is all this exercises — so after the burst we get 429.
+func TestWebAuthnBeginRateLimited(t *testing.T) {
+	t.Parallel()
+	for _, path := range []string{"/api/register/begin", "/api/login/begin"} {
+		t.Run(path, func(t *testing.T) {
+			t.Parallel()
+			_, _, ts, h := splitServer(t)
+
+			var got429, gotAllowed bool
+			for i := 0; i < 15; i++ {
+				resp := post(t, ts, h.auth, path, url.Values{})
+				resp.Body.Close()
+				if resp.StatusCode == http.StatusTooManyRequests {
+					got429 = true
+				} else {
+					gotAllowed = true
+				}
+			}
+			if !gotAllowed {
+				t.Fatalf("%s: every request throttled; burst should allow some through", path)
+			}
+			if !got429 {
+				t.Fatalf("%s: never returned 429; the rate limiter is not wired", path)
+			}
+		})
+	}
+}
+
 // assertAccountOK asserts a 303 back to /account carrying a success ("ok") flash.
 func assertAccountOK(t *testing.T, resp *http.Response, label string) {
 	t.Helper()